• 한국융합학회논문지
• /
• 제10권11호
• /
• pp.345-352
• /
• 2019

본 연구는 부정사건이 발생한 기업을 대상으로 기업내부 관계자의 기회주의적 행태에 대하여 살펴보고 정보우위에 의한 지분변화가 자본시장에서의 시장퇴출 가능성과 지니는 관련성에 대한 실증분석을 실시하였다. 연구결과는 다음과 같이 요약된다. 먼저 사건 전후에 나타난 기업내부자의 지분감소가 큰 기업의 경우 공시이후에 보다 큰 음(-)의 초과 수익률이 나타나고 있다. 사건 기업 중 향후 시장퇴출로 이어진 기업집단에서는 뚜렷한 지분감소현상이 나타나고 있으며 비교집단 간 차이검정에서 통계적으로 유의한 결과를 보여주고 있다. 로짓회귀분석 결과 지분변화의 회귀계수가 음(-)의 통계적으로 유의한 결과 값을 나타내어 내부관계자의 지분감소가 클수록 향후 시장퇴출가능성이 증가하고 있음을 확인하였다. 이러한 연구결과는 정보우위에 따른 정보거래 가능성을 보여주는 결과로써, 자본시장 내외부자간 정보비대칭 현상에 대한 학술적 근거가 될 뿐만 아니라 이해관계자들의 의사결정에 유용한 정보를 제공해줄 수 있을 것으로 기대된다.

• 한국철도학회논문집
• /
• 제20권3호
• /
• pp.320-328
• /
• 2017

철도차량에 폭 넓게 적용되고 있는 축상고무스프링의 노화에 따른 탈선안전도 영향을 분석하고자 노화 축상고무스프링 시료를 대상으로 특성시험을 수행하였다. 그리고 축상고무스프링 노화가 탈선 안전에 미치는 영향을 분석하기 위하여 주행 동특성 해석을 수행하였다. 사용연수 17년이 지난 롤고무 축상스프링 시료를 대상으로 한 상하방향 특성시험결과, 고무 노화로 인하여 변위 복원기능이 저하되었고 스프링강성이 현저히 증가하였다. 그리고 EN14363규격 적용 twist궤도 주행 시를 모사한 주행동특성 해석결과, 정상 차량모델(Case1)에 비하여 노화 축상스프링 특성을 적용한 차량모델(Case2)의 탈선계수와 윤중감소가 증가하여 탈선안전도는 저하하였다. 특히 급격한 선형 변동이 발생하는 천이구간 주행 시 윤중감소로 인한 탈선안전도는 취약하게 나타났다.

• 설비공학논문집
• /
• 제18권4호
• /
• pp.312-319
• /
• 2006

In this study, performance of 2 pure hydrocarbons and 7 mixtures was measured in an attempt to substitute HCFC22 used in air-conditioners and heat pumps. The mixtures were composed of R1270 (propylene), R290 (propane), HFC152a, and RE170 (Dimethyl ether, DME). The pure and mixed refrigerants tested have GWPs of $3{\sim}58$ as compared to that of $CO_2$ and the mixtures are all near-azeotropic showing the gliding temperature difference (GTD) of less than $0.6^{\circ}C$. Thermodynamic cycle analysis was carried out to determine the optimum compositions and actual tests were performed in a laboratory heat pump test bench at the evaporation and condensation temperatures of 7.5 and $45.1^{\circ}C$ respectively. Test results show that the coefficient of performance (COP) of these mixtures is up to 5.7% higher than that of HCFC22. While propane showed 11.5% reduction in capacity, most of the fluids tested had the similar capacity to that of HCFC22. Compressor discharge temperatures were reduced by $11{\sim}17^{\circ}C$ with these fluids. There was no problem with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 55% as compared to HCFC22. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for. residential air-conditioning and heat pumping application.

• 대한한방부인과학회지
• /
• 제28권1호
• /
• pp.85-91
• /
• 2015

Objectives: Postmenopausal symptoms are subject to many factors. Recently, obesity has been suggested as a factor of hot flush. So this study aims to report the relationship between body composition and Menopause Rating Scale (MRS), The Menopause-specific Quality of Life Questionnaire (MENQOL) of postmenopausal women. Methods: We studied 42 climacteric women who had visited Kyung Hee University Hospital at Gangdong from April 2011 to July 2014. 42 women had filled out MRS, MENQOL, and they had taken body composition tests. Pearson correlation tests were conducted. (Correlation was statistically significant at the 0.05 level) Results: Correlation between psychological subscale of MENQOL and Waist-Hip Ratio (WHR) was statistically significant (pearson correlation coefficient=0.385; p-value=0.012). But other subscales of MRS and MENQOL were not statistically related with body composition. Conclusions: WHR could be an important factor of psychological health of menopausal women. So, abdominal fat reduction must be considered when curing menopausal symptoms. In connection with climacteric depression, well-designed studies would be necessary.

• Archives of Pharmacal Research
• /
• 제24권6호
• /
• pp.568-571
• /
• 2001

The purpose of this work was to study the effect of storage time and temperature on the in vitro release kinetics of a commercial sustained-release dosage form of theophylline, at different pHs of the dissolution medium. The formulation was stored at $35^{\circ}C$ for 16 months and at $45^{\circ}C$ for 8 months, with a relative humidity of 60%. The in vitro release tests were performed at pHs 2, 4, 6 and 7.4. The mean values of the transport coefficient n, were close to 0.5 in all the conditions tested, which indicates that the transport system is not modified after storage of the formulation at $35^{\circ}C$ and $45^{\circ}C$. The mean values of the dissolution rate constant ranged from 0.036 to 0.043 $min^{-n}$, under all the conditions tested. Significant differences (${\alpha}=0.05$) were found between pHs 2, 4 and 6, 7.4 for all the model-independent parameters studied. When the formulation was kept at $35^{\circ}C$ for 16 months, the mean percentage of drug dissolved at 8 hours was 25.61% (pHs 2, 4) and, 36.12% (pHs 6, 7.4), representing a 26% and 24% reduction, respectively. Simitar results were obtained after storing the formulation at $45^{\circ}C$ for 8 months, corresponding to 33.3% (pHs 2, 4) and, 22.5% (pHs 6, 7.4) diminution, respectively. The values of the similarity factory $f_2$, obtained were lower than 50, which indicates the lack of similarity among the dissolution profiles, after storing the formulation under the experimental Conditions tested.

• Tribology and Lubricants
• /
• 제34권6호
• /
• pp.217-225
• /
• 2018

In this study, we spray a Ni-Cr composite powder onto AISI 4340 steel using the high velocity oxygen fuel method. We subsequently subject the Ni-Cr coating (as-sprayed) to ultrasonic nanocrystal surface modification (UNSM) process to improve the tribological performance. This study aims at increasing the wear resistance and durability of the Ni-Cr coating by altering the surface integrity and microstructure via the UNSM process. The UNSM process reduces the surface roughness of the as-sprayed coating by about 64%, which is explained by observing the elimination of high peaks and valleys and filling up micro-pores. Furthermore, a change in the microstructure of the coating due to continuous high-frequency strikes to the surface by a tip can lead to an increase in hardness from about 48 to 60 HRC. Furthermore, we investigate the characterization of the friction and wear behavior of Ni-Cr coating by a ball-on-disc tribometer in the dry conditions. We determine that after the UNSM process, there is a significant reduction in the friction coefficient of the as-sprayed coating from approximately 1.1 to 0.75. This is owing to the increased hardness and smoothed surface roughness. In addition, we investigate the surface morphology and wear track of the coatings before and after the UNSM process using a scanning electron microscope, energy dispersive spectrometer, and three-dimensional laser scanning microscope. We observe that the wear track of the Ni-Cr coating after the UNSM process is lower than that of the as-sprayed one. Thus, we confirm that the UNSM process has a significant influence on the improvement of the tribological performance of the Ni-Cr composite coating.

• 대한토목학회논문집
• /
• 제41권5호
• /
• pp.523-531
• /
• 2021

일반적으로 기초는 여러 개의 단일말뚝이 상부 구조체에 의해 연결된 상태로 군말뚝을 의미한다. 하지만, 군말뚝에 상부 하중 재하 시 지반에 작용하는 응력 범위는 단일말뚝에 비해 더 넓은 폭과 깊이로 확장되고, 중복되기 때문에 전체적인 지지력은 감소할 수 있다. 이러한 지지력 감소비를 군말뚝 효율이라 하나 일반적인 말뚝과 지반의 접촉 조건에 따른 영향을 분석한 연구는 부족한 실정이다. 따라서 본 연구에서는 지반 구성 및 군말뚝의 배치, 간격, 지반과 말뚝간의 접촉 특성을 해석 변수로 설정하고, 군말뚝 효율 및 군말뚝을 구성하는 개별말뚝의 거동을 분석하였다. 해석 결과, 지반 종류에 따라 마찰계수 증가 시 군말뚝 효율은 수렴 또는 감소하는 경향을 보였으며, 이를 통해 최적 군말뚝 효율을 분석하였다. 또한, 개별말뚝 분석을 통한 하중 감소비 파악 결과, 군말뚝 내부에 위치한 말뚝의 경우 하중을 상대적으로 적게 받았으며, 이는 내부 지반에 대한 영향인 것으로 판단된다.

• 한국재료학회지
• /
• 제29권3호
• /
• pp.150-154
• /
• 2019

This study investigates the effect of MnO2 and CuO as acceptor additives on the microstructure and piezoelectric properties of $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$, which has a rhombohedral-tetragonal phase boundary composition. $MnO_2$ and CuO-added $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$ ceramics sintered at a relatively low temperature of $1020^{\circ}C$ show a pure perovskite phase with no secondary phase. As the addition of $MnO_2$ and CuO increases, the sintered density and grain size of the resulting ceramics increases. Due to the difference in the amount of oxygen vacancies produced by B-site substitution, Cu ion doping is more effective for uniform grain growth than Mn ion doping. The formation of oxygen vacancies due to B-site substitution of Cu or Mn ions results in a hardening effect via ferroelectric domain pinning, leading to a reduction in the piezoelectric charge coefficient and improvement of the mechanical quality factor. For the same amount of additive, the addition of CuO is more advantageous for obtaining a high mechanical quality factor than the addition of $MnO_2$.

• Tribology and Lubricants
• /
• 제34권6호
• /
• pp.241-246
• /
• 2018

This research addresses the improvement of tribo-systems, specifically regarding the reduction of friction and wear through tribo-coupling between tetrahedral amorphous carbon (ta-C) with different types of counterpart materials, namely bearing steel (SUJ2), tungsten carbide (WC), stainless steel (SUS304), and alumina ($Al_2O_3$). A second variable in this project is the utilization of different values of duct bias voltage in the deposition of the ta-C coating - 0, 5, 10, 15, and 20 V. The results of this research are expected to determine the optimum duct bias and best counter materials associated with ta-C to produce the lowest friction and wear. Results obtained reveal that the tribo-couple between the ta-C coating and SUJ2 balls produces the lowest friction coefficient and wear rate. In terms of duct bias changes, deposition using 5 V produces the most optimum tribological behavior with lowest friction and wear on the tribo-system. In contrast, the tribo-couple between ta-C with a WC ball causes penetration through the coating surface layer and hence high surface delamination. This study demonstrates that the most effective ta-C coating duct bias is 5 V associated with SUJ2 counter material to produce the lowest friction and wear.

• Wind and Structures
• /
• 제29권4호
• /
• pp.247-270
• /
• 2019

Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.